The problem of finding the quantum theory of the gravitational field, and th...nding what is quantum spacetime, is still open. One of the most active of th...on of a spacetime ``foam''. Long standing open p...verview of ideas, techniques, results and open...

01:30:15Thanks Jonathan I can't help it, I was about to log off, but I love this...dinal invariants, but some basic questions have remained open d...this problem in ZFC as well as of an a priori unrelated open...

You dirty rat -- I feel your pain. "Though empathetic behavior has been observed anecdotall...r device -- a closed tube with a door that can be nudged open f...al daily restraint sessions, the free rat learned how to open...